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ABSTRACT: a b s t r a c t a r t i c l e i n f o Available online 29 December 2011 Keywords: Nanodiamond film Oxidation UV/ozone XPS SEM Contact angle UV/ozone irradiation was designed for controllable oxidation of nanodiamond films with distinctive chemical species. XPS investigation revealed that various kinds of oxygen-related chemical components would be functionalized onto nanodiamond surface covered by selective liquids for UV/ozone treatment. And the results of contact angle tests were in good accordance with the oxygen contents revealed from the deconvoluted C 1 s peaks. The covered solution on the nanodiamond film was found to be one significant factor besides UV/ozone illumination. Surface chemical components and the wettability were proved to be closely dependent on the covered liquids on the UV/ozone treated nanodiamond surface. Without any cover solution, heavy defects would be induced on nanodiamond via direct UV/ozone irradiation. However, basic solution rich with OH anions would be taken as an effective way for controllable oxidation, achieving high percentage of COOH but less defects on the nanocrystalline diamond surface. This controllable oxidation strategy would be widely applied for controllable surface modification of nanodiamond films in the device field.
Diamond and Related Materials 12/2011; 24:146-152. · 1.91 Impact Factor
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ABSTRACT: Applying the hydrogen (H) radical exposure at the last step of MOSFET fabrication process, an oxygen (O)-terminated channel was converted to a H-terminated one to obtain subsurface hole accumulation for field-effect transistor operation. Low-resistive titanium carbide (TiC) source/drain and alumina gate oxide were resistant to the hydrogenation process. The shallow TiC side contacts (~ 3 nm in depth) to the hole accumulation layer (channel) showed good ohmic contacts with a specific contact resistance of 2 X 10<sup>-7</sup>-7 X 10<sup>-7</sup> ¿·cm<sup>2</sup>. For diamond MOSFETs with the TiC ohmic layer, the saturated maximum drain current and maximum transconductance reached 160 mA/mm and 45 mS/mm, respectively. An fT of 6.2 GHz and an f <sub>max</sub> of 12.6 GHz were obtained. The hydrogenation-last approach is a nondestructive method for the fabrication of diamond MOSFET with high production yield.
IEEE Transactions on Electron Devices 06/2010; · 2.32 Impact Factor
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ABSTRACT: Chemical trends of Schottky barrier heights of ten kinds of metal contacts on hydrogen-terminated diamond (001) surfaces are estimated from the temperature dependence of their current-voltage characteristics. In addition to the measurements, the interface of the metal/hydrogen-terminated diamond is theoretically modeled including the carrier density of the surface conductive layer and the electron-affinity variation from the clean surface of the hydrogen-terminated diamond. Based on the model, a relation among the carrier density, the electron affinity variation, and the barrier heights are derived. The relation explains well experimental results of and other than the present work.
Phys. Rev. B. 01/2010; 81(4).
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K Ishizaka,
R Eguchi,
S Tsuda,
A Chainani,
T Yokoya,
T Kiss,
T Shimojima,
T Togashi,
S Watanabe,
C-T Chen,
Y Takano,
M Nagao,
I Sakaguchi,
T Takenouchi, H Kawarada,
S Shin
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ABSTRACT: Laser-excited photoemission spectroscopy is used to show that the doped carriers in metallic or superconducting diamond couple strongly to the lattice via high-energy (approximately 150 meV) optical phonons, with direct observations of localized Franck-Condon multiphonon sidebands appearing as Fermi-edge replicas. It exhibits a temperature-dependent spectral weight transfer from higher to lower energy sidebands and zero-phonon Fermi-edge states. The quantified coupling strength shows a systematic increase on lowering temperature, implicating its relation to the normal state transport and superconductivity.
Physical Review Letters 04/2008; 100(16):166402. · 7.37 Impact Factor
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ABSTRACT: We evaluated diamond metal oxide semiconductor field effect transistors (MOSFETs) on (001) homoepitaxial and (110) preferentially oriented large-grain diamond films with an Al<sub>2</sub>O<sub>3</sub> gate insulator and demonstrated their improved DC and RF characteristics (I<sub>DS</sub> = -790 mA/mm and f<sub>T</sub> = 45 GHz, which are the highest values for diamond FETs). Channel mobility evaluation and load-pull measurement were carried out for the first time for diamond MOSFETs. Even on a large-grain diamond substrate, a high channel mobility of 120 cm<sup>2</sup>/Vs was obtained. This is comparable to that of a SiC inversion layer. A power density of 2.14 W/mm was obtained at 1 GHz. This power density exceeded those of Si LDMOSFETs and GaAs FETs.
Electron Devices Meeting, 2007. IEDM 2007. IEEE International; 01/2008
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H. Okazaki,
T. Yokoya,
J. Nakamura,
N. Yamada,
T. Nakamura,
T. Muro,
Y. Tamenori,
T. Matsushita,
Y. Takata,
T. Tokushima,
S. Shin,
Y. Takano,
M. Nagao,
T. Takenouchi, H. Kawarada,
T. Oguchi
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ABSTRACT: We have performed soft X-ray angle-resolved photoemission spectroscopy (SXARPES) of a heavily boron-doped superconducting diamond film (T-c = 7.2 K) in order to Study the electronic structure near the Fermi level (E-F). Careful determination of measured momentum space that across F point in the Brillouin zone (BZ) and increase of an energy resolution provide further spectroscopic evidence that EF is located at the highly dispersive diamond-like bands, indicating that holes at the top of the diamond-like valence band play an essential role for the conducting properties of the heavily boron-doped superconducting diamond for this boron-doping region (effective carrier concentration of 1.6%). The SXARPES intensities at E-F were also mapped out over BZ to obtain experimental Fermi surface sheets and compared with calculations. Crown Copyright (c) 2008 Published by Elsevier Ltd. All rights reserved.
Journal of Physics and Chemistry of Solids. 01/2008; 69:2978-2981.
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ABSTRACT: Diamond metal-insulator-semiconductor field-effect transistors (MISFETs) with a 0.1 mum gate length were fabricated on high quality IIa-type polycrystalline diamond. A maximum drain current density of 650 mA/mm and a cut-off frequency (f<sub>T</sub>) of 42 GHz were obtained. The drain current density is the highest value reported to date for diamond FETs.
Power Semiconductor Devices and IC's, 2007. ISPSD '07. 19th International Symposium on; 06/2007
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K Ishizaka,
R Eguchi,
S Tsuda,
T Yokoya,
A Chainani,
T Kiss,
T Shimojima,
T Togashi,
S Watanabe,
C-T Chen,
C Q Zhang,
Y Takano,
M Nagao,
I Sakaguchi,
T Takenouchi, H Kawarada,
S Shin
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ABSTRACT: We investigate the temperature (T)-dependent low-energy electronic structure of a boron-doped diamond thin film using ultrahigh resolution laser-excited photoemission spectroscopy. We observe a clear shift of the leading edge below T=11 K, indicative of a superconducting gap opening (Delta approximately 0.78 meV at T=4.5 K). The gap feature is significantly broad and a well-defined quasiparticle peak is lacking even at the lowest temperature of measurement (=4.5 K). We discuss our results in terms of disorder effects on the normal state transport and superconductivity in this system.
Physical Review Letters 02/2007; 98(4):047003. · 7.37 Impact Factor
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T Yokoya,
E Ikenaga,
M Kobata,
H Okazaki,
K Kobayashi,
A Takeuchi,
A Awaji,
Y Takano,
M Nagao,
I Sakaguchi,
T Takenouchi, H Kawarada,
T Oguchi
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ABSTRACT: Hard x-ray photoemission spectroscopy has been used to study intrinsic core-level electronic structure evolution of heavily boron-doped superconducting diamond films made with a microwave plasma-assisted chemical-vapor deposition method. The boron concentration dependent C 1s core-level spectra show system-atic changes in the shift of the main peak and in the evolution of an additional feature at 1.1– 1.3 eV lower binding energy than the main peak. In comparison to a low boron concentration nonsuperconducting diamond, the higher boron concentration doped diamond films show formation of several additional features in the B 1s core levels. Based on the present results, the local chemical environments around the doped boron atoms, the efficiency of hole doping by boron doping, and the implications for a recent x-ray absorption study are discussed.
PHYSICAL REVIEW B 75, 205117. 01/2007;
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ABSTRACT: We have investigated the superconductivity discovered in boron (B)-doped
diamonds by means of 11B-NMR on heteroepitaxially grown (111) and (100) films.
11B-NMR spectra for all of the films are identified to arise from the
substitutional B(1) site as single occupation and lower symmetric B(2) site
substituted as boron+hydrogen(B+H) complex, respectively. A clear evidence is
presented that the effective carriers introduced by B(1) substitution are
responsible for the superconductivity, whereas the charge neutral B(2) sites
does not offer the carriers effectively. The result is also corroborated by the
density of states deduced by 1/T1T measurement, indicating that the evolution
of superconductivity is driven by the effective carrier introduced by
substitution at B(1) site.
11/2006;
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ABSTRACT: In this framework, it has been discovered that boron-doped diamond can also become a superconductor below critical temperatures Tc well above the liquid helium temperature. The strongly covalent bonds, the high concentration of impurities, and the high energy of its optical phonon in comparison with the Fermi energy, make diamond much different from the conventional metals where the BCS theory of superconductivity holds. Here the reflectivity of superconducting diamond is measured down to sub-terahertz frequencies. Our results consistently indicate that diamond, in spite of the above cited peculiarities, behaves as a BCS superconductor in the "dirty" regime.
Infrared Millimeter Waves and 14th International Conference on Teraherz Electronics, 2006. IRMMW-THz 2006. Joint 31st International Conference on; 10/2006
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ABSTRACT: Heavily boron-doped, diamond films can become superconducting with critical temperatures Tc well above 4 K. Here we first measure the reflectivity of such a film down to 5 cm(-1), by also using coherent synchrotron radiation. We thus determine the optical gap 2Delta, the field penetration depth lambda, the range of action of the Ferrell-Glover-Tinkham sum rule, and the electron-phonon spectral function alpha2F(omega). We conclude that diamond behaves as a dirty BCS superconductor.
Physical Review Letters 10/2006; 97(9):097002. · 7.37 Impact Factor
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ABSTRACT: Diamond metal-insulator-semiconductor field-effect-transistors (MISFETs) utilizing a hole accumulation layer have been fabricated on a hydrogen-terminated (H-terminated) diamond surface. The highest cut-off frequency (f<sub>T</sub>) of 30 GHz and the maximum frequency of oscillation (f<sub>max</sub>) of 60 GHz were obtained in the 0.35 mum gate diamond MISFET. RF power operations of diamond MISFETs were demonstrated for the first time. In RF power operation, the high power density of 2.14 W/mm was obtained at 1 GHz
Power Semiconductor Devices and IC's, 2006. ISPSD 2006. IEEE International Symposium on; 07/2006
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ABSTRACT: We observe strong softening of optical phonon modes in superconducting (Tc = 4.2 K) boron doped diamond near the Brillouin zone center using inelastic x-ray scattering from a CVD-grown highly oriented sample. The magnitude of the softening, and our observation that it becomes stronger approaching zone center, supports theoretical models suggesting a phonon-mediated pairing mechanism via coupling of optical phonon modes to Fermi surfaces around the zone center. The electron-phonon coupling parameter is determined as approximately lambda= 0.33.
01/2006;
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K. Ishizaka,
R. Eguchi,
S. Tsuda,
T. Kiss,
T. Shimojima,
T. Yokoya,
S. Shin,
T. Togashi,
S. Watanabe,
C.-T. Chen,
C.Q. Zhang,
Y. Takano,
M. Nagao,
I. Sakaguchi,
T. Takenouchi, H. Kawarada
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ABSTRACT: We have investigated the low-energy electronic state of boron-doped diamond thin film by the laser-excited photoemission spectroscopy. A clear Fermi-edge is observed for samples doped above the semiconductor–metal boundary, together with the characteristic structures at possibly due to the strong electron–lattice coupling effect. In addition, for the superconducting sample, we observed a shift of the leading edge below Tc indicative of a superconducting gap opening. We discuss the electron–lattice coupling and the superconductivity in doped diamond.
Science and Technology of Advanced Materials. 01/2006;
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ABSTRACT: The physical properties of lightly doped semiconductors are well described by electronic band-structure calculations and impurity energy levels. Such properties form the basis of present-day semiconductor technology. If the doping concentration n exceeds a critical value n(c), the system passes through an insulator-to-metal transition and exhibits metallic behaviour; this is widely accepted to occur as a consequence of the impurity levels merging to form energy bands. However, the electronic structure of semiconductors doped beyond n(c) have not been explored in detail. Therefore, the recent observation of superconductivity emerging near the insulator-to-metal transition in heavily boron-doped diamond has stimulated a discussion on the fundamental origin of the metallic states responsible for the superconductivity. Two approaches have been adopted for describing this metallic state: the introduction of charge carriers into either the impurity bands or the intrinsic diamond bands. Here we show experimentally that the doping-dependent occupied electronic structures are consistent with the diamond bands, indicating that holes in the diamond bands play an essential part in determining the metallic nature of the heavily boron-doped diamond superconductor. This supports the diamond band approach and related predictions, including the possibility of achieving dopant-induced superconductivity in silicon and germanium. It should also provide a foundation for the possible development of diamond-based devices.
Nature 01/2006; 438(7068):647-50. · 36.28 Impact Factor
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Chemical Vapor Deposition 03/2005; 11(3):127 - 130. · 1.80 Impact Factor
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ABSTRACT: Using a highly conductive p-type layer appearing on a hydrogen terminated diamond surface, surface channel field effect transistors (FETs) have been developed. This type of FET is applicable in high-frequency devices operating at high power, biosensors in electrolyte solution, and quantum devices such as single-hole transistors fabricated by surface nanotechnology.
Advances in Carbon Electronics, 2004. The Third International Seminar on; 11/2004
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ABSTRACT: Submicrometer-gate (0.2-0.5-μm) diamond metal-insulator-semiconductor field-effect transistors (MISFETs) were fabricated on an H-terminated diamond surface. The maximum transconductance in dc mode reaches 165 mS/mm, while the average transconductance is 70 mS/mm in submicrometer-gate diamond MISFETs. The highest cutoff frequency of 23 GHz and the maximum frequency of oscillation of 25 GHz are realized in the 0.2-μm-gate diamond MISFET. From the intrinsic transconductances or the cutoff frequencies, the saturation velocities are estimated to be 4×10<sup>6</sup> cm/s in the submicrometer-gate FETs. They are reduced by gate-drain capacitance and source resistance.
IEEE Electron Device Letters 08/2004; · 2.85 Impact Factor
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ABSTRACT: Diamond has always been adored as a jewel. Even more fascinating is its outstanding physical properties; it is the hardest material known in the world with the highest thermal conductivity. Meanwhile, when we turn to its electrical properties, diamond is a rather featureless electrical insulator. However, with boron doping, it becomes a p-type semiconductor, with boron acting as a charge acceptor. Therefore the recent news of superconductivity in heavily boron-doped diamond synthesized by high pressure sintering was received with considerable surprise. Opening up new possibilities for diamond-based electrical devices, a systematic investigation of these phenomena clearly needs to be achieved. Here we show unambiguous evidence of superconductivity in a diamond thin film deposited by a chemical vapor deposition (CVD) method. Furthermore the onset of the superconducting transition is found to be 7.4K, which is higher than the reported value in ref(7) and well above helium liquid temperature. This finding establishes the superconductivity to be a universal property of boron-doped diamond, demonstrating that device application is indeed a feasible challenge.
07/2004;
